1. Field of the Invention
The invention relates to a process for preparing unsaturated organosilicon compounds containing organic carbonyloxy groups in the presence of tertiary phosphines.
2. Description of the Related Art
Silicon compounds containing unsaturated organic carbonyloxy functions, e.g. 3-methacryloxypropyl-trimethoxysilane, are widely employed as bonding agents between inorganic and organic materials, e.g. in sizes for glass fibers, or as crosslinkers in organic polymers.
Various methods of preparing such compounds are known. Thus, for example, DE 2851456 C2 describes the hydrosilylation of chlorosilanes containing SiH bonds by means of unsaturated organic molecules such as allyl methacrylate in the presence of metal catalysts to form chlorosilanes containing corresponding unsaturated organic functional groups. The disadvantage of this process is the fact that the subsequent alcoholysis step necessary to obtain the corresponding alkoxy-functionalized silanes cannot be carried out continuously in most cases because of the high tendency of the unsaturated organic function to polymerize. Apart from this process, the direct reaction of an alkoxysilane containing SiH bonds with unsaturated organic molecules in the presence of metal catalysts is also known, e.g. from DE 38 32 621 C1. However, this process has the serious disadvantage that some of the alkoxysilanes necessary for carrying out the process are highly toxic and tend to decompose and therefore involve particular safety risks.
In the case of the processes described, for example, in EP 242 627 A2 and EP 437 653 B1, on the other hand, the compounds described are obtained by a nucleophilic substitution reaction between a metal or ammonium salt of an unsaturated organic acid and a haloorganofunctionalized silane. Here, the salt of the unsaturated organic acid is obtained in various ways. In the process described in EP 242 627 A2, the unsaturated organic acid is reacted with a tertiary amine to give the ammonium salt which can immediately be reacted in the same reaction vessel with the haloorganosilicon compound. However, a disadvantage is the low reactivity of the ammonium salts of unsaturated organic acids, which leads to very long reaction times and thus to a serious risk of polymerization of the product. Two alternative methods are described in EP 437 653 B1: in one process, the isolated sodium or potassium salt of the unsaturated organic acid is used. This has the disadvantage that this salt firstly has to be synthesized in a dedicated process and dried in a costly fashion. Alternatively, the metal salt of the unsaturated organic acid can be obtained by reaction of the corresponding metal alkoxide in the corresponding alcohol by reaction with the unsaturated organic acid. After addition of the haloorganofunctionalized silicon compound and removal of the alcohol by distillation, the reaction can then be carried out in the same reaction vessel. This process has the disadvantage that the metal alkoxides used are generally corrosive, highly reactive and very expensive and, in addition, large amounts of the respective, sometimes toxic, alcohol are required as solvent, which significantly reduces the attractiveness of this process. EP 1 249 454 A1 describes a process for preparing unsaturated organosilicon compounds having carbonyloxyorganic groups in the presence of phosphonium salts as phase transfer catalysts. The disadvantage of this process is that the catalysts used are very expensive and are usually solids, which makes their metering considerably more difficult.